Darren Douglas, 46, left the Spring Hill open prison in Buckinghamshire, early Sunday morning as did Ricardo Dunn, 32, who is serving an indeterminate sentence after being convicted of grievous bodily harm with intent after assaulting a man in a street fight in 2009.

Douglas is serving a life sentence for stabbing a man to death outside a pub in 1998. During his trial, Douglas was described as a "man with a very short fuse" as he confronted his victim in the bathroom and accused him of being "queer." He then forced him outside for a fight but pulled a knife from his pocket and stabbed him seven times -- at least twice through the victim's heart.

Police say Douglas should not be approached.

"We are keen to speak to anyone who may have seen these men in the area and can provide us with information about their movements," Chief inspector Olly Wright, of Thames Valley Police, said, according to the Daily Mail. "These men were both convicted for violent offenses and I would advise anyone who sees them, to not approach them and call police immediately.

"Both men have links with other areas so may have travelled out of the Thames Valley to those areas," Wright added. "I would like to remind people that it is a criminal offense to harbor these men and anyone caught doing so would be arrested."

According to Wikipedia, an open prison is "an informal description applied to any penal establishment in which the prisoners are trusted to serve their sentences with minimal supervision and perimeter security and are not locked up in prison cells. Prisoners may be permitted to take up employment while serving their sentence.

"In the UK, open prisons are often part of a rehabilitation plan for prisoners moved from closed prisons. They may be designated 'training prisons' and are only for prisoners considered a low risk to the public."